i think you want to setup a software raid, as fakeraid requires a motherboard bios that is capable of it, and you would be limiting the size of your drive to the smallest in the array (so your 2tb drive, would only be 1tb, and it will erase the drives clean.)
as for software raid, i've never set one up in linux, i've only done hardware and fake raid installations.
usb external drives have always been slow, i don't think you will see much of a boost in speed by going to ext3/4, and i think if you go software raid, it would drastically decrease your performance in linux.
there are several tools at your leisure that are available for linux tho, for backing up.
there is the formidable rsync, that you can setup in a cron job, that will at first make a mirror back up of your main drive, keeping permissions intact and file structure. after the first back up, it will then only back up files if changes are made to them and any new files (which will greatly increase the speed of the back ups.)
then there is tar, which is a compression program, that you can set to a cron job, that will "zip" your file system onto the external drive, there are several ways to do this, but it will back up the entire system, not just files that have changed since last back up.
there are several things you will need to take into account when you build any sort of cron job back up script, there are several folders in the linux filesystem you will not want to back up, as they are virtually populated and have drastically inflated space used (which more than likely stall any system if you try to back up these folders.), you will also want to avoid backing up the back up drive as well (it will enter into a loop trying to back it up, and more than likely crash or stall the system.)
i'm honestly not aware of any programs that are specifically designed to full back ups like this in linux, other than the two i've mentioned (which aren't really designed for this sole purpose, but will do the task that is needed.)
i will make a suggestion, that rsync is the better option here, and instead of backing up the entire installation, just backing up the /home folder might be the wiser course of action.
edit: here is a link on how to do a software raid for ubuntu 11.04
i do not vouch for the validity of this how to, other than it is on the ubuntu community site. i also take no responbility for misuse of the information contained in it or data loss that is suffered from it
.Edited by Transhour - 10/2/11 at 9:42am